1. Field of the Invention
This invention relates to primer compositions. More particularly, this invention relates to a primer composition that cohesively bonds a silicone rubber, especially a fluorosilicone rubber, to the surface of various substrates, including metals.
2. Description of the Prior Art
Primers have heretofore been required to cohesively bond or coat materials, including polyolefins, polyamides, organic rubbers such as EPDM and DPR, and silicone rubbers, to the surface of glasses, metal oxides and metals. Canadian Pat. No. 837,650 describes vinyltris(t-butylperoxy)silane as an example of a primer employing an organoperoxide. This primer is less than satisfactory due to the requirement for hot pressing at an elevated temperature for an extended period of time. Also, the adhesion with a variety of bonding agents is inadequate. For this reason, several methods for improving this primer have been proposed.
One such method is disclosed in Japanese Pat. No. 75/35530, which discloses a primer composition containing vinyltris(t-butylperoxy)silane, an organoperoxide with a half-life of 1 minute at from 130.degree. to 190.degree. C., and an inert organic solvent. Hot pressing is accomplished at lower temperatures in a shorter period of time then required in the aforementioned Canadian patent, however, this composition does not provide adequate bonding for adherends such as silicone rubber and particularly fluorosilicone rubbers.
The preceding shortcomings are rectified by the present inventors' invention described in U.S. Pat. No. 4,534,815, which issued on Aug. 13, 1985. This patent teaches using primer composition containing an alkoxy group-containing organosilicon compound, vinyltris(t-butylperoxy)silane and an organic solvent to bond silicone rubber to substrates and, in particular, to achieve good bonding between fluorosilicone rubbers and substrates.
Compounds wherein the vinyl radical of vinyltris(t-butylperoxy)silane is replaced with a saturated hydrocarbon radical generally provide poor bonding for silicone rubbers compared with vinyltris(t-butylperoxy)silane. These compounds have therefore been used heretofore in the silicone rubber industry.
An objective of the present invention is to provide a primer for cohesively bonding silicone rubbers, particularly fluorosilicone rubbers, to substrates. A second objective is to provide a primer having an extended life, excellent bonding properties following a short period of heating or hot pressing at relatively low temperatures, optionally under pressure, and no odor emission in order to avoid adversely affecting the working environment.